Telephone transmitter



May23, 1939. E, G DANIELscN TELEPHONE TRANSIITTER Filed Jan. 20, 1936 2Sheets-Sheet l y 4555 25 da 2a /5 .57M 42A" .Fr'llE-E- INVENTOR. /ffnes/C?. an/'e/sof? BY @Mam ATTORNEX,

May 23 l939- E, G DANll-:LsoN 2,159,628

TELEPHONE TRANSIITTER Filed Jan. 20, 1936 2 Sheets-Sheet 2 Patented May23, 1939 UNITED STATES PATENT OFFICE TELEPHONE TRANSMITTER Ernest G.Danielson, San Francisco, Calif., al-v aignor to Bemler Company Ltd.,San Francisco. Calif., a corporation of California Application January20, 1938, Serial No. 59,877

3 Claims, (Ol. 179-111) This invention relates generally to the conasFig. 3, and showing certain parts in cross struction of telephonetransmitters such as are section. used in conjunction with radiobroadcast equip- Flg. 5 is a cross sectional detail taken along ment andpublic address systems. More particutheline 5 5 of Fig. 3, but on asmaller scale. 5 larly it relates to telephone transmitters of the Fig.6 is a cross sectional detail taken along the condenser type in which athin metal diaphragm line l-SofFig. 3, and on the same scale as Fig. 5.or electrode, adapted to be vibrated by sound Fig. 'l is a crosssectional view taken along the waves, is in capacitative relationshipwith an asline 1-1 ofl Fig. 3, and onthe same scale as Figs. sociatedrigid electrode or back plate. 5 and 6. Y' *k `It is an object of theinvention to generalhr The transmitter illustrated in the drawings 10improve upon the method and means employed consists of a thin metaldiaphragm I0, which is for producing and maintaining optimumtensiontensioned across one face of a shell Ii. An inner ing o f thinmetal diaphragms employed in teleannular member or ring- I2 cooperateswith the phone transmitters. In the past, the methods shellii in amanner to be presently explained, to l5 and means employed for thispurpose have not maintain the diaphragm i0 properly tensioned. l5

been satisfactory, in that it has been diillcult if In a transmitter ofthe condenser type dianot impossible to uniformly tension the dia-Dhragm I0 forms a vibratory electrode, responphragm in all.directions,to a point near the sive to sound waves, while a button-likestrucelastic limit of the material. Lack of uniform ture i3 immediatelybehind the diaphragm I0, tension, or lack of tension to the properdegree, Serves aS a rigid electrode 01- back plate. With 20 3 isdetrimental to fidelity, in addition to the fact respect to thematerials utilized, it is desirable to that ununiform tension frequentlycauses meform the diaphragm l0 0f astronglight alloy like chanicalfailure. The present invention makes duralumin having a thickness in theorder of one possible uniform tensioning of the diaphragm in thousandthof an inch. A similar alloy is suitall directions,without manufacturingdifficulties, able fOr fOrming the Shell ll. and the inner 25 'and witha predetermined degree of tension ring |2- which approaches the elasticlimit of the mate- The preferred manner in which the shell ii rial. andring i2 are adapted to tension the dia- A further object of theinvention is to improve Dhragm l0 during assembly, and t0 maintain uponthe manufacture and construction of rigid tension to the desired degree,can be described 30 o electrodes or back plates, such as are employed aSfollowst- Shell il lS fOrrned t0 provide a in telephone transmitters ofthe condenser type. substantially cylindrical inner surface Il, which Inthe past, such electrodes have been made of iS aCOntinuatiOn 0f theannular bevelled Surmetal, and have required careful and expensive facei6. The forward face of the shell is provided machining operations toproduce the desired with an lnturned portion i'|,`to form an annular 35form. The present invention dispenses with the Shoulder Il which thediaphragm l0 engages. T0 use of machined metal, and employs a moldablethe rear of the bevelled surface I6 the shell is material such as a.condensate product, which is formed t0 provide an annular abutment 0rshoulmolded to substantially gna] form v der I9, which forms a stop forlimiting movement o Additional objects of the invention, including 0fthe m13 l2 ln one lll'ectlon- 0 Ring I2 is provided with a cylindricalsurface the provision of a simplified and novel-assembly, will appearfrom the following description in which the preferred embodiment of theinvention of ring n 1S rounded as indicated at z2 while has been setforth in dem 1n conjunction with the rear portion is enlarged to afforda shoulder 45 the accompanylng drawings' 23, for engaging the shoulderi9 of the shell,

Referring to the drawings: l The thin sheet metal of which the diaphragmFlg l l5 a' front eleva'llolla'l Vlew' lllllsl'latlllg a is constructedis initially cut to a diameter sub telephone transmitter incorporationgthe present Stanuauy larger than the diameter of the Cynp- 2i, which isdlmensioned to fit tightly within the cylindrical surface I4. Theforward end edge lnventlon drical surface il. This circular blank isthen 50 Fig. 2 is a side view of the transmitter as illusplaced upon therear face of the shell Il, with trated in Fig. 1. its center concentricwith the axis of the shell. Fig. 3 is a cross-sectional view taken alongthe By means of a suitable assembling machine, ring line 3 3 of Fig. l,but on an enlarged scale. l2 is then advanced uponv the diaphragm, withFig. 4 is an fexploded view on the same scale the result that as thering enters the shell, the 55 edge portion of the diaphragm is bentrearwardly. As the ring commences to telescope.

with the cylindrical surface I4 o'f the shell, the peripheral edgeportion of the diaphragm is tightly gripped, as illustrated in Fig. 4.Additional advancing movement of the ring I2 accomplishes substantiallya drawing operation upon the peripheral edge portion of the diaphragm,with the result that the margin of the diaphragm is drawn tosubstantially cylindrical form. The drawing operation causes a certainamount of tightening of the diaphragm, but it is not tensioned to adegree desired in the final assembly. As the ring I2 is advanced to itsiinal assembled position illustrated in Fig. 3, the diaphragm contactsthe annular shoulder I8, and thereafter a lateral distortion of thediaphragm occurs, without slippage of the marginal portion of thediaphragm with respect to the ring I2. When shoulders I9 and 23 comeinto engagement, the diaphragm has been tensioned to the degree desired,to a point near the elastic limit of the material.

In Fig. 3 the drawn marginal edge of the diaphragm has been designatedby numeral 26, and is relatively frce of folds such as might causeuneven gripping. During the assembly operation just described it isdesirable to heat-the shell I I to an elevated temperature, so that itwill subsequently shrink and more effectively grip the margin of thediaphragm. vLikewise in order to safeguard against slippage of themargin of the diaphragm with respect to ring I2, during the finaltensioning of the diaphragm, the ring can be provided with a series ofannular grooves 21.

The button-like structure I3 is annular in contour, and of such adiameter as to fit loosely within the ring I2. It is formed as anintegral body of suitable molded material, such as a phenolic or ureacondensate. The outer peripheral portion 28 is electricallynon-conductive, while the inner portion 29 is provided with anelectrically conductive planar surface 3|. Surface 3| is in relativelyclose parallel relationship With the adjacent side of diaphragm I0, asfor example a clearance on the order of one thousandth of an inch. Inthis connection note that the clearance as illustrated in Fig. 3 hasbeen exaggerated, for purposes of clarity.

In order to provide proper acoustical characteristics the portion 29 isprovided with a series of openings 32, a suitable arrangement of whichis illustrated in Fig. 7. The conductice face 3I is also interrupted bya series of grooves or channels 33, which communicate with the openings32. Such an arrangement of openings and channels permits escapement ofgas from the relatively thin di-electric film interposed between thediaphragm and the conductive face 3I. The forward annular face 34 of theperipheral portion 28, is in engagement with the rear face of thediaphragm I0, and therefore serves to maintain the desired clearancebetween the conductive face 3I, and the diaphragm.

In forming the button-like structure I3 as de-v scribed above, it ismolded to substantially final form. In other words the openings 32, aswell as the channels 3I, are provided by virtueof the character of themolds or dies employed, instead of being machined into the bodyafter'the molding operatin..v The., conductive surface 3I can be formedbyany one of a number of different methods. The preferred method is toform the intermediate portion 29"of the body, of a homogeneous mixtureof condensate material and termed an acoustical valve.

electrically conductive particles, as for example carbon or graphite.This can be readily done by making up two pellets for the moldingoperation, one being a disc-like pellet containing condensate materialmixed with a divided'conductive material like carbon or graphite, andthe other being an annular ring-like pellet formed only of condensatematerial, with possibly a non-conductive ller medium. For the moldingoperation these pellets are placed concentrically within the formingdie, and upon being compressed in conjunction with heat, the material ofthe two pellets fuses together to form an integral final body. After themolding operation, it is only necessary to machine off and polish thesurface 3I, so that the desired clearance will be afforded with respectto the diaphragm I0. As an alternative procedure the body can be moldedto substantially complete form, using ordinary condensate materials, andthe surface 3I then covered with a thin sheet of metal or likeconductive material, by electro-plating or by a sputtering process. Thisconductive surface can then be machined and polished, to afford thedesired degree of accuracy.

Assuming that the preferred procedure is employed for making thebutton-like structure I3, a lead wire 36 can be embedded in theconductive portion 29, and is shown extending to the rear side forconvenient electrical connection.

For completing the assembly, a closure disc 31 is shown extending overthe rear side of the shell II. This closure plate carries the terminalscrews 38 and 39, with the terminal 39 being insulated by bushing 4I.Extending adjacent the inner face of the closure plate 31, there is aflexible diaphragm 42, formed of suitable material such as an imperviousdi-electric cloth. The peripheral margin of diaphragm 42 is showninterposed between the rear end face of ring I2 and the adjacentmarginal face of the closure platel 31. It is also shown aperturedcentrally to accommodate screw 39, with the annular portion immediatelysurrounding such opening gripped between the inner face of bushing 4I,and a washer 43. The plate 31 is clamped to its desired position, bysuitable means such as an annular threaded ring 44. The space betweenthe inner face of plate 31, and the diaphragm 42, is exposed toatmospheric pressure, through duct 46.

The button-shaped 4structure I3, is retained in proper assembledrelationship, with respect to the diaphragm I0 yand ring I2, by suitablemeans such as an annular' spring clip 41. The notched periphery 48 ofthis clip is adapted to engage within a groove 49, formed in ring I2,while the inner periphery engages the adjacent rear face of thebutton-like structure I3, to urge this struc* ture towards the diaphragmI0.

In order to minimize distortion dueto cavity resonance, a device 5I isemployed, which can be This device can be made of pressed sheet metal,in the form of a Shallow cup, which is seated within the annular .recess52, formed on the rear side of the strucatmosphere of suitable inertgas, such as nitrogen. This can be done by introducing nitrogen gasthrough the opening 55, through terminal 39, before final tightening ofthe threaded ring M. After this operation opening 55 is sealed, andthereafter flexing of diaphragm 42 equalizes the pressure within thetransmitter, with the pressure of the external atmosphere.

The simplicity of the completed assembly will be apparent from the abovedescription. The arrangement' utilized for tensioning the diaphragm Idispenses with the use of conventional bolts and like clamping devices,and makes possible a more compact structure, having superior acousticalcharacteristics because of the absence of cavity resonance. Although thediaphragm is tensioned to a relatively high degree, the fact that thetension is adequately distributed in all directions minimizes breakage,both during manufacture and assembly, and during usage. Use of themolded button-like structure I3 greatly simpliles manufacturingproblems, because the openings 30,2 and particularly the channels 33,need not be formed by accurate machining methods, such as have been usedin the past.

I claim:

1. In a telephone transmitter of the condenser type wherein a vibratableelectrode is disposed in close spaced relationship with one face of astationary electrode, a relatively flat lrigid body formed integrally ofmolded condensate` material, a portion of the body intermediate itsperipheral edge portion being formed of a homogeneous mixture ofcondensate material and divided conductive particles, whereby saidintermediate portion is rendered electrically conductive to serve assaid stationary electrode, the peripheral edge portion of the body beingnon-conductive.

2. In a telephone transmitter of the condenser ype wherein a vibratableelectrode is disposed in close spaced relationship with one face of astationary electrode, a relatively at rigid body formed integrally ofmolded condensate material, a portion of the body intermediate itsperipheral edge portion being formed of a homogeneous mixture ofcondensate material and electrically conductive particles, whereby saidintermediate portion is electrically conductive to serve as saidstationary electrode, said intermediate portion also having openingstherein and having one side face for cooperation with said vibratableelectrode, the peripheral edge portion of the body being non-conductive.

3. An electrode for a telephone transmitter of the condenser type,comprising a relatively flat rigid body formed integrally oi moldedcondensate material, a portion of the body intermediate its peripheraledge portion comprising a homogeneous mixture of condensate material andelectrically'conductive particles, whereby said intermediate portion isrendered electrically conductive, said intermediate portion havingopenings therein and having one planar side face, said side face beinginterrupted by grooves which communicate with said openings, theperipheral edge portion of the body being electrically non-conductive.

ERNEST G. DANIEL-SON.

